The invention relates generally to electronic power conversion and more particularly to a power converter using nonlinear composite film capacitors constructed from polymer anti-ferroelectric (AFE) particle composites as energy storage components.
The task of power converters utilizing power electronics technology generally is directed to processing and controlling the flow of electric energy by supplying voltages and currents in a form that is optimally suited for user loads. Power electronics is recognized as a significant technology propelling many critical areas of technology such as, without limitation, telecommunications, computers, automation and process control, robotics, transportation, and all forms of environment-friendly energy conversion.
One major factor associated with power converter design relates to the selection of available high power density components. Power capacitors permit electrical energy to be stored over a long time period and released as required in a controlled manner, and thus are regarded as major passive components used in power converters. User-driven requirements for such capacitors may include, for example, electrical characteristics such as capacitance, voltage rating, current handling rating, parasitic behaviors such as equivalent series resistance (ESR), equivalent series inductance (ESL), etc. User-driven requirements may further include, for example, mechanical characteristics such as size, shape, and weight. Environmental characteristics may also be considered. Environmental characteristics may include, for example, temperature range, vibration, life expectancy, etc.
The most frequently used capacitor technologies in modern power converters include electrolytic capacitors and electrostatic capacitors (ceramic and polymer film). Electrolytic capacitors offer the highest capacitance value and appear to be the likeliest choice for low-voltage high-current circuits. Electrolytic capacitors are however, limited in use due to power inefficiency (large ESR), lower operation frequency (large ESL), and limited temperature range. Electrostatic capacitors however, offer very good high frequency performance due to low ESR and low ESL, but are generally limited in use due to low capacitance values. Ceramic capacitors tend to crack due to mechanical stress which is the primary failure mode associated with use of ceramic material(s). Local failure(s) caused by defects in fabrication processes may induce catastrophic failures of ceramic capacitors.
Power converter input voltage is generally in the form of a 50 Hz or 60 Hz singe wave AC voltage provided by an electric utility that is first converted by the power converter to a DC-link voltage. The instantaneous input power generally contains large pulsation components while the output power is usually constant for most applications. The power is generally unbalanced over half the line cycle. This unbalanced power has to be stored in an energy storage element such as a capacitor. Since the DC-link voltage should be as ripple free as possible, bulk capacitors are required on the DC side. Studies have shown that more than 40% of a power converter volume is associated with the power converter capacitor elements.
In view of the foregoing, it would be advantageous to provide a power converter having capacitive storage elements that consume substantially less than 40% of the overall power converter volume, while simultaneously improving high frequency performance, reducing temperature rise characteristics or increase in operational temperatures, and increasing functionality of voltage clamping capability beyond that achievable with power converters that employ conventional electrolytic and/or electrostatic storage capacitors. It would also be advantageous if the capacitive storage elements provided mechanical reliability and coercive field strength levels not achievable with ceramic capacitors or capacitors using ceramic materials.